Fuels which are liquid at ambient handling temperatures, such as liquid hydrocarbons e.g. kerosene, gasoline and diesel, can become contaminated with water, such as from condensation formed within a storage tank vented to the atmosphere and solids particulates, such as rust and metallic particles derived from storage vessels and pipelines, and silicate particles transported as dust in the atmosphere and introduced into the fuel through the venting of storage vessels.
A liquid fuel must pass stringent quality testing to ensure it is suitable for use in an engine, as contaminants such as water and solid particles can be detrimental to the performance of the engine or even damaging to the engine. Quality tests include measuring the amount of particulate solids contained in the fuel.
To reduce solid particulate contaminants from a fuel, the fuel is typically passed through a filter before it is conveyed or otherwise transported to a storage vessel at or near to a vehicle fuelling station. However, such filtering does not eliminate all solids contaminants, as fine particles can pass through the filter without being caught, and breakdown of the filter itself can generate solid particles in the fuel.
As the colloidal or dispersed water is in the form of tiny droplets the machine used to detect the particles cannot distinguish between solid particulates and the water droplets. This may lead to an artificially high count suggesting the fuel is unusable. By removing the water droplets in a sample of the fuel an accurate particle count can be determined. This allows the fuel to be distributed without the need for expensive treatment and storage.
Attempts to remove the water by use of solvents have been undertaken (see, for example, U.S. Pat. No. 6,064,480—Mountain et al, EP-A-1715323—Clarke et al). However, the use of solvents requires significant quantities to be added requiring the results be adjusted due to dilution. Naturally the use of flammable solvents is also not desirable in a field application. Field trials using both the composition of this invention and standard solvents such as Isopropyl alcohol have found that at dispersed water contamination levels up to 100 ppm the solvent system requires as much as 2.5 times the quantity of this invention to solvate the water. It must be noted that in the case of the solvents the grade used must be as analytically pure as possible with no dissolved water and <100 counts/ml of particulate>4 μm(c). These grades must be stored in as dry as condition as possible as they are generally hygroscopic in nature.
Water-in-oil microemulsions can be formed, where emulsifies are mixed with oil and water so as to distribute the water as a microemulsion in the oil. The water-in-oil emulsions formed must render the droplet size of the dispersed water phase preferably at no greater than 0.1 μm. This forms a clear and bright translucent fluid that allows the light detection of the particle counting equipment to pass through without interference (see e.g. GB2463030—Martin). Typically the lower limit of the particle counting machine is 4 μm(c). However, should the droplet size of the emulsion be greater than the wavelength of the light used, the fluid may appear hazy and the opportunity for droplet coalescence and ultimately particle counting interference will occur.
Verdegan, B M; Thibodeau, L: “Particle counting oil and water emulsions” Particulate Science And Technology, vol. 7, no. I, 1989, pages 23-34 demonstrates the use of a single surfactant, Aerosol OT, as being capable at sufficient levels to remove any contaminant water by forming emulsions. However, the method of use and preparation is cumbersome and not applicable to actual in-field use. The surfactant must be heated in the fuel to 60° C. and allowed to cool. Heating the fuel in the field is not a practical method and creates an unnecessary fire risk.
US200910194480 (Daniel et al) discloses a method of identifying contaminants within a liquid hydrocarbon media containing contaminants. The method includes adding an optical tag to a water wash, adding the tagged water wash to the liquid hydrocarbon media, emulsifying the liquid hydrocarbon media and analysing the contaminants in the hydrocarbon media with a microscope.
US2009/0319195 (Hoots et al) discloses a method of monitoring and optimizing the concentration of an additive composition in a fuel ethanol, wherein a component in the additive composition is capable of providing a fluorescent signal. Based upon the measured fluorescent signal, the concentration of the additive composition in the fuel ethanol may be adjusted. The additive compositions disclosed in Hoots, such as corrosion inhibitors, are all liquids.
WO2012/050844 (Conroy et al) provides a method of detecting/quantifying a fluorescent taggant in a liquid sample. The method may be used to detect an adulteration of gasoline and diesel fuels.
Most engines are designed to accommodate a low level of fine inorganic particles, such as those particles which are not extracted from the fuel by filtering. However, solids particles generated by breakdown of the filter can be much more problematical: whilst subsequent filtering can eliminate the larger filter breakdown particles, the smaller filter-breakdown particles are not captured and can be carried in the fuel along with the fine inorganic particles.
Filters used for removing solids particles from liquid fuels such as jet fuel are typically made from super absorbent polymers (SAPs), which are organic polymers. Such organic polymers often comprise pendant carboxyl groups. It is known that jet fuels contaminated with filter breakdown material have caused aircraft incidents, as the organic polymer particles have migrated during the refuelling of an aircraft into the main fuel tanks and subsequently interfered with fuel flow, which ultimately resulted in the loss of engine performance. The most notable incident attributed to migration of SAP filter breakdown particles was that in Surabaya (13 Apr. 2010—Accident Bulletin 1/2011). Without wishing to be bound by theory, it is believed that the SAP particles may have agglomerated in the fuel tanks and the larger particles so formed causing blockages in or residues on the aircraft fuel monitoring and control systems.
Various methods have been proposed for determining whether a liquid fuel is suitable for use in an engine by measuring the amount of contaminants in the fuel. In these methods, the fuel is either rejected or accepted for use in the engine depending upon whether or not the amount of contaminants in the fuel is above or below a predetermine standard amount.
A jet fuel, for example, may be rejected or accepted, depending upon whether the total amount of solids particles exceeds a minimum specified amount. It is therefore necessary to have accurate and fast methods for analysing the amount of solids particles in the fuel. However, the filtering methods employed do not distinguish between organic and inorganic solids in the fuels, let alone to distinguish the amounts of potentially harmful organic particulate solids that may subsequently agglomerate in the fuel from all the other particulate solids that may be present in the fuel in an amount which, as a total, may be considered an acceptable amount.
It is an object of the present invention to provide an accurate and fast method of determining the presence of an amount of SAP particles as a contaminant in a fuel and, in so doing, provide a method of determining whether the fuel is suitable for use in an engine.